Class: Fontisan::Tables::VariationCommon::ItemVariationData

Inherits:
Binary::BaseRecord
  • Object
show all
Defined in:
lib/fontisan/tables/variation_common.rb

Overview

Item variation data

Contains delta values for a set of items. Each item can have deltas for multiple regions.

Instance Method Summary collapse

Methods inherited from Binary::BaseRecord

#raw_data, read, #valid?

Instance Method Details

#delta_sets ⇒ Array<Array<Integer>>

Parse delta sets for all items

Returns:

  • (Array<Array<Integer>>) —

    Delta sets for each item



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# File 'lib/fontisan/tables/variation_common.rb', line 145

def delta_sets
  return @delta_sets if @delta_sets
  return @delta_sets = [] if item_count.zero?

  data = raw_data
  # Delta data starts after header and region indices
  offset = 6 + (region_index_count * 2)

  # Each item has region_index_count deltas
  # short_delta_count are int16, rest are int8
  long_count = region_index_count - short_delta_count

  # Safety check: long_count should not be negative
  if long_count.negative?
    warn "ItemVariationData parsing error: short_delta_count (#{short_delta_count}) > region_index_count (#{region_index_count})"
    return @delta_sets = []
  end

  @delta_sets = Array.new(item_count) do |i|
    item_offset = offset + (i * (short_delta_count * 2 + long_count))

    # Read short deltas (int16)
    shorts = Array.new(short_delta_count) do |j|
      delta_offset = item_offset + (j * 2)
      next nil if delta_offset + 2 > data.bytesize

      # Signed 16-bit
      value = data.byteslice(delta_offset, 2).unpack1("n")
      value > 0x7FFF ? value - 0x10000 : value
    end.compact

    # Read long deltas (int8)
    longs = Array.new(long_count) do |j|
      delta_offset = item_offset + (short_delta_count * 2) + j
      next nil if delta_offset + 1 > data.bytesize

      # Signed 8-bit
      value = data.byteslice(delta_offset, 1).unpack1("C")
      value > 0x7F ? value - 0x100 : value
    end.compact

    shorts + longs
  end
end

#region_indices ⇒ Array<Integer>

Parse region indices

Returns:

  • (Array<Integer>) —

    Region indices



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# File 'lib/fontisan/tables/variation_common.rb', line 127

def region_indices
  return @region_indices if @region_indices
  return @region_indices = [] if region_index_count.zero?

  data = raw_data
  offset = 6 # After header fields

  @region_indices = Array.new(region_index_count) do |i|
    idx_offset = offset + (i * 2)
    next nil if idx_offset + 2 > data.bytesize

    data.byteslice(idx_offset, 2).unpack1("n")
  end.compact
end